Newcastle disease virus (NDV) is the model for important, but difficult to study paramyxoviruses like measles, mumps, and respiratory syncytial viruses. It also remains an avian pathogen which produces frequent devastating epizootics in poultry flocks throughout the world. In this proposal we utilize mutants and revertants and monoclonal antibodies to explore NDV's three membrane proteins (HN, F and M); particular emphasis will be placed on HN. These proteins have multiple functions, some of which have been clearly defined and others of which have not. We will attempt to assign protein(s) to functions where this hasn't been done and locate functional areas as well as monoclonal antibody binding sites on the molecules. Using wild type NDV, AV-WT, we will fragment HN, identify peptides and sites of disulfide bonds or glycosylation, and sequence important peptides. Comparing AV-WT and mutant proteins we will map mutations. We will use monoclonal antibodies to these proteins in functional inhibition and peptide binding studies to locate functional areas. We will also use monoclonal antibodies to probe changes in mutant protein binding sites, and in the case of anti-HN antibodies, to select site-specific mutants with alterations in regions important to infectivity. As mutants and antibodies to F become available, we will conduct similar studies on F. Finally, we will conduct additional studies on mutants and revertants to confirm the assignment of group D mutants to the M protein. We will probe previously undetected processing of the HN protein and examine HN's role(s) in hemolysis and infectivity.